1. Field of the Invention
This invention relates to novel esters of laidlomycin which are used to increase the feed efficiency in ruminants and to treat coccidiosis in domestic animals, especially in chickens.
2. Prior Art
The antibiotic laidlomycin is a known compound which inhibits the growth of some Gram-positive bacteria. See The Journal of Antibiotics, Vol. XXIX, No. 7, pp. 759-761, July, 1976 and Vol. XXVII, No. 11, pp. 884-888, Nov. 1974. Monensin is also a known antibiotic and has been shown to be useful in increasing feed utilization in ruminants. See for example, U.S. Pat. No. 3,794,732. The structure of each of these compounds is shown in Formula (I), below, wherein for laidlomycin R is propionate and A is hydrogen, for monensin (Factor A) R is methoxy and A is methyl, and for monensin (Factor B) R is methoxy and A is hydrogen. ##STR2##
As discussed in the above-mentioned U.S. Pat. No. 3,794,732, it is important to increase the efficiency of feed utilization in domestic animals, especially meat producing and milk producing animals such as cattle. Carbohydrates form a large part of these animals' diets, and the efficiency of carbohydrate utilization is desirably increased by treatments which encourage intraruminal production of propionate rather than acetate from the carbohydrates. The theory behind this is discussed in the '732 patent and is incorporated herein by reference.
The improved efficiency of feed utilization resulting from the use of compounds described by Formula (I), above, can be determined by observing an increased concentration or molar percentage of propionate in the rumen.
Surprisingly, it has now been discovered that the laidlomycin esters of this invention exhibit an unexpectedly superior increase in the molar percentage of propionate produced by rumen microorganisms as compared to laidlomycin or the sodium salt thereof. It has also been found that the compounds of this invention inhibit lactic acid production better than laidlomycin or its sodium salt.